The Design of Rolling Bearing Mountings Part 11 pdf

92 Double toggle jaw crusher Double toggle jaw crushers have a large mouth open- ing. They are used, for example, as primary crushers to prepare ballast for road building. The coarse crushing is followed by further crushing operations until an ag- gregate of the size and shape required, e.g. gravel or grit, is obtained. Operating data Input power 103 kW; speed of eccentric shaft n = 210 min –1 ; mouth opening 1,200 x 900 mm; eccentric radius 28 mm. Bearing selection, dimensioning The pitman is fitted to the eccentric part of the hori- zontal shaft and actuates the swing jaw through a dou- ble toggle lever system. The inner bearings supporting the pitman must accommodate heavy crushing loads. The outer bearings transmit, in addition to these loads, the flywheel weight and the circumferential loads resulting from the drive. Due to the high loading and the rugged operation, spherical roller bearings are chosen. Spherical roller bearings FAG 23260K.MB are mounted as outer bearings and FAG 23176K.MB as inner bearings. The pitman bearing arrangement is of the floating bearing type. The outer bearing arrange- ment features a locating bearing at the drive side and the floating bearing at the opposite side. With an index of dynamic stressing f L ≈ 4.5 the bearing arrangement is safely dimensioned with regard to nominal rating life. Machining tolerances The bearings are mounted on the shaft with adapter sleeves FAG H3260HGJ and FAG H3176HGJ, re- spectively. The bearing seats on the shaft are machined to h7 with a cylindricity tolerance IT5/2 (DIN ISO 1101), and the bores of housing and pitman to H7. Lubrication, sealing Grease lubrication with a lithium soap base grease of penetration class 2 wit EP additives (FAG rolling bear- ing grease Arcanol L186V). The relubrication interval for the bearings is 2 3 months. The bearings are sealed by multiple labyrinths. Once or twice a week, fresh grease is injected into the laby- rinths. 92: Bearing mounting of a double-toggle jaw crusher Locating bearing Floating bearing Swing jaw Eccentric shaft Pitman 93 Hammer mill Hammer mills are mainly used for crushing ores, coal, and stone. Operating data Hourly throughput 90 120 t of iron ore; input power 280 kW; rotor speed 1,480 min –1 , rotor weight includ- ing hammers approximately 40 kN; bearing centre dis- tance 2,000 mm. Bearing selection Due to the high loads and rugged operation, hammer mill rotors are mounted on spherical roller bearings. This self-aligning bearing type can compensate for mis- alignments of the two plummer block housings, and possible rotor deflections. Two spherical roller bearings FAG 23228EASK.M.C3 are mounted, one acting as the locating bearing, the other one as floating bearing. The increased radial clearance C3 was selected because of the high speed. The bearing inner rings heat up more than the outer rings, causing the bearing clear- ance to be reduced during operation. Bearing dimensioning The rotor weight imposes a radial load on the bearings. Added to this are unbalanced loads and shock loads whose magnitude can only be estimated. These loads are introduced in the nominal rating life calculation by multiplying the rotor weight G R with a supplementary factor f z of 2.5 3, depending on the operating condi- tions. The thrust loads acting on the bearings are so small they need not be taken into account in the life calculation. With the dynamic load rating C = 915 kN, the speed factor f n = 0.32 (n = 1,480 min –1 ) and the rotor weight G R = 40 kN, the index of dynamic stressing f L for one bearing: f L = C · f n / (0.5 · G R · f z ) = 915 · 0.32 / (20 · 3) = 4.88 An f L value of 3.5 4.5 is usually applied to hammer mills. Thus the bearings are adequately dimensioned with regard to nominal rating life (L h approximately 100,000 h). Bearing mounting The bearings are mounted on the rotor shaft with withdrawal sleeves FAG AHX3228. They are fitted into plummer block housings MGO3228K. Both housings (open design) are available for locating bear- ings (design BF) and for floating bearings (design BL). The split housings of series MGO were especially de- veloped for mill applications. They are designed for oil lubrication and feature particularly effective seals. Machining tolerances For mounting with sleeves, the shaft seats are machined to h7, with a cylindricity tolerance IT5/2 (DIN ISO 1101). The housing bores are machined to G6. Thus the requirement that the outer ring of the floating bear- ing must be displaceable within the housing is met. Lubrication, sealing For reliable operation at high speeds, the bearings are oil bath lubricated. Grease-packed labyrinths prevent the ingress of foreign matter. To increase the sealing efficiency, grease is replenished frequently. Flinger grooves on the shaft, and oil collecting grooves in the housing covers retain the oil within the housing. 93: Hammer mill mounting Locating bearing Floating bearing 94 Double-shaft hammer crusher Double-shaft hammer crushers are a special type of hammer crushers or hammer mills. They feature two contra-rotating shafts to which the hammers are at- tached. This type is especially suitable for crushing large-sized material with a high hourly throughput and optimum size reduction. Operating data Hourly thoughput 350 400 t of iron ore; input pow- er 2 x 220 kW; rotor speed 395 min –1 , rotor weight in- cluding hammers 100 kN; bearing centre distance 2,270 mm. Bearing selection Due to the rugged operation, spherical roller bearings are mounted which can compensate for misalignment between the two plummer blocks and for shaft deflec- tions. Bearing dimensioning In addition to the loads resulting from the rotor weight, the bearings have to accommodate loads re- sulting from imbalances and shocks. They are taken into account by multiplying the rotor weight G R by the supplementary factor f z = 2.5. Small thrust loads need not be taken into account in the life calculation. The shaft diameter at the bearing locations determines the use of one spherical roller bearing FAG 23234EASK.M at each side. For the moderate speeds of this application normal radial clearance CN is satis- factory. With the dynamic load rating C = 1,370 kN, the speed factor f n = 0.476 (n = 395 min –1 ) and the rotor weight G R = 100 kN, the index of dynamic stressing f L per bear- ing: f L = C · f n /(0.5 · G R · f z ) = 1,370 · 0.476/(50 · 2.5) = 5.2 With this f L value, which corresponds to a nominal rat- ing life L h of approximately 120,000 hours, the bear- ings are very adequately dimensioned. Bearing mounting The bearings are mounted on the rotor shaft with withdrawal sleeves FAG AH3234 and mounted in FAG plummer block housings BNM3234KR.132887. One of the plummer blocks is designed as the floating bearing (closed on one side, design AL), the other one as the locating bearing (continuous shaft, design BF). The unsplit housings of series BNM were developed especially for hammer mills and crushers. They were designed for grease lubrication (grease valve) and feature particularly effective seals. Machining tolerances The shaft seats are machined to h7, with a cylindricity tolerance IT5/2 (DIN ISO 1101). The housing bores are machined to H7; this allows the outer ring of the floating bearing to be axially dis- placed. Lubrication, sealing Grease lubrication with FAG rolling bearing grease Arcanol L71V is satisfactory for the speeds in this example. Relubrication is required at certain intervals. A grease valve protects the bearing against over-lubrica- tion. Due to the adverse ambient conditions a double- passage labyrinth seal is provided. Frequent grease re- plenishment to the labyrinths improves sealing effi- ciency. 94: Double-shaft hammer crusher Floating bearing Locating bearing 95 Ball tube mill Tube mills are mostly used in the metallurgical, min- ing and cement industries. The tube mill described is used in an Australian gold mine for grinding aurifer- ous minerals (grain sizes 4 30 mm) into grit by means of grinding bodies (balls). The grain size of the materi- al depends on the number of balls and the quantity of added water. The grinding drum, which revolves around its horizontal axis, is lined with chilled-cast iron plates. Charged with the grinding stock, it is very heavy. Operating data Drum: diameter 5,490 mm, length 8,700 mm; input power 3,850 kW; speed 13.56 min –1 ; drum mass when loaded 400 t; maximum radial load per bearing F r = 1,962 kN; maximum thrust load F a = 100 kN; bearing distance 11,680 mm, throughput 250 t/h. Bearing selection Trunnion bearings As the drum rotates, the bearings have to accommo- date, in addition to the heavy weight, constant shock- type loads caused by the grinding bodies. Both drum trunnions are supported on spherical roller bearings of series 239, 248 or 249. The bearings compensate for static and dynamic misalignments that can be caused by misalignments of the bearing seats (large bearing distance) or drum deflections. In this example, spheri- cal roller bearings with a tapered bore (K 1:30), FAG 248/1500BK30MB are mounted both as the locating bearing at the drive end and as the floating bearing at the feed end. The bearings are mounted on the trun- nion with a wedge sleeve. Drive pinion bearings The drive pinion is supported on two spherical roller bearings FAG 23276BK.MB with adapter sleeve FAG H3276HG, in plummer block housings with Taconite-seals FAG SD3276TST. Bearing dimensioning The dimensioning of the drum bearings is based on half the weight of the loaded drum (400/2 · 9.81 = 1,962 kN). The shock loads are taken into account by a shock fac- tor f z = 1.5. The required nominal rating life is 100,000 h; this corresponds to an index of dynamic stressing f L = 4.9. The equivalent dynamic load P = f z · F r + Y · F a = 2 · 1.5 · 1,962 + 4.5 · 100 = 3,393 kN With a dynamic load rating C = 12,900 kN the index of dynamic stressing: f L = C/P · f n = 12,900/3,393 · 1.31 = 4.98 (L h > 100,000 h). The bearings are very safely dimensioned with regard to nominal rating life. The bearings are mounted in split FAG plummer block housings SZA48/1500HF (locating bearing) and SZA48/1500HL (floating bearing). The outer rings are tightly fitted into shell sleeves (e.g. made of grey-cast iron) in the lower housing half. They facilitate com- pensation of axial length variations. The sliding effect is enhanced by grease injected into the shell sleeve/housing joint. Machining tolerances The circumferentially loaded inner rings are press-fitted on the trunnion. This is easily achieved by mounting them hydraulically on wedge sleeves. The radial clear- ance reduction and the radial clearance of the mounted bearing have to be observed (see table in FAG cata- logue WL 41 520, chapter on spherical roller bear- ings). The trunnions are machined to h9, with a cylindricity tolerance IT5/2 (DIN ISO 1101); the housing bores to H7. Lubrication, sealing Grease lubrication with a lithium soap base grease of penetration class 2 with EP additives, e. g. FAG rolling bearing grease Arcanol L186V. Continuous replenish- ment (approx. 5 g/h per bearing) ensures adequate lu- brication. The bearings are sealed by multiple labyrinths. Due to the extreme ambient conditions, the labyrinths are preceded by dirt baffle plates and rubbing seals (V- rings). This combination is also referred to as Taconite sealing. The labyrinths are also continuously replen- ished with approx. 5 g/h per labyrinth. 95: Ball tube mill mounting 96 Support roller of a rotary kiln Rotary kilns for cement production can extend over a length of 150 m or more. The support rollers are spaced at about 30 m intervals. Operating data Kiln outside diameter 4.4 m; support roller diameter 1.6 m; support roller width 0.8 m; radial load per support roller 2,400 kN; thrust load 700 kN. Speed 5 min –1 ; mass of support roller and housing 13 t. Bearing selection, dimensioning For such rotary kilns FAG offers complete assemblies consisting of a twin housing SRL, the support roller with axle LRW, and the bearings. In this example the two support-roller bearings are mounted into split plummer block housings with a common base (frame) made of grey-cast iron. Spherical roller bearings FAG 24184B (dynamic load rating C = 6,200 kN) are mounted in a floating bearing arrangement, i. e. the shaft can be displaced relative to the housing by a de- fined axial clearance. In addition to the radial loads, the spherical roller bearings accommodate thrust loads resulting from dis- placements of the rotary kiln. With an index of dynamic stressing f L = 4.9, correspond- ing to a nominal rating life L h = 100,000 h, the bear- ings are adequately designed. Machining tolerances Shaft to n6 (circumferential load on inner ring); hous- ing bore to H7. Lubrication, sealing Grease lubrication with a lithium soap base grease with EP additives (e. g. rolling bearing grease Arcanol L186V). At the roller side the bearings are sealed with felt strips and grease-packed labyrinths. 96: Support roller of a rotary kiln Vibrating machines Vibrating screens are used for conveying and grading bulk material. They operate in mines, quarries, stone crushing plants and foundries, in the foodstuff and chemical industries, and in many other preparation and processing plants. The main vibrating screen types are: two-bearing screens with circle throw, two-bearing screens with straight-line motion, and four-bearing screens. Vibrator motors and vibrating road rollers also come under the category of vibrating machines. Selection of bearing type and bearing design Rolling bearings in vibrating screens are stressed by high, mostly shock-type loads. To compound matters, the bearings, while rotating about their own axis, per- form a circular, elliptical or linear vibrating motion. This results in high radial accelerations (up to 7 g) which additionally stress the bearings, and especially the cages. High operating speeds, usually with inaccu- rately aligned bearing locations, and pronounced shaft deflections are additional requirements which are best met by spherical roller bearings. For these adverse operating conditions FAG spherical roller bearings with reduced bore and outside diameter tolerances and an increased radial clearance are used: The FAG standard design E.T41A is used for shaft di- ameters of 40 150 mm. The centrifugal forces of the unloaded rollers are accommodated by two pressed- steel, window-type cages and radially supported by a cage guiding ring in the outer ring. Shafts with diameters of 160 mm and more are sup- ported on vibrating screen bearings A.MA.T41A. These bearings have a fixed centre lip on the inner ring and retaining lips on both sides. The split machined brass cage is of the outer-ring riding type. Bearing dimensioning Vibrating screen bearings which are comparable with field-proven bearings can be dimensioned on the basis of the index of dynamic stressing f L , provided that the boundary conditions are comparable as well. f L values between 2.5 and 3 are ideal. 97 Two-bearing screen with circle throw Operating data Screen box weight G = 35 kN; vibration radius r = 0.003 m; speed n = 1,200 min –1 ; number of bearings z = 2 ; acceleration due to gravity g = 9.81 m/s 2 . Bearing dimensioning Two-bearing screens work beyond the critical speed; thus the common centroidal axis of the screen box and the unbalanced load does not change during rotation. The bearing load due to the screen box centrifugal force is: F r = 1/z · G / g · r · (π · n/30) 2 = = 1/2 · 35 / 9.81 · 0.003 · (3.14 · 1,200/30) 2 = 84.5 kN To allow for the unfavourable dynamic stressing, the bearing load should be multiplied by the supplemen- tary factor f z = 1.2. Thus, the equivalent dynamic load P = f z · F r = 1.2 · 84.5 = 101.4 kN With the index of dynamic stressing f L = 2.72 (L h = 14,000 h) and the speed factor f n = 0.34 (n = 1,200 min –1 ) the required dynamic load rating C = f L /f n · P = 2.72/0.34 · 101.4 = 811.2 kN The recommended index of dynamic stressing f L for vibrating screens is 2.5 3, corresponding to a nominal fatigue life L h of 11,000 to 20,000 hours. Spherical roller bearings FAG 22324E.T41A with a dynamic load rating of 900 kN are chosen. Machining tolerances The eccentric shaft features two spherical roller bear- ings, one as the locating bearing, the other as floating bearing. The inner rings are point loaded and mounted with a shaft tolerance of g6 or f6. The outer rings are circumferentially loaded and fitted tightly in the hous- ing bore to P6. Lubrication, sealing Circulating oil lubrication. Mineral oils with a mini- mum viscosity of 20 mm 2 /s at operating temperature are recommended. The oil should contain EP additives and anti-corrosion additives. Outer sealing is provided by a grease-filled, replenish- able labyrinth. A flinger ring with an oil collecting groove prevents oil leakage. A V-ring is provided between flinger ring and labyrinth to separate oil and grease. 12 1 Festlager Ll 97: Two-bearing screen with circle throw Floating bearing Locating bearing [...]... revolution of the eccentric shafts For calculation of these loads, the distance R between the centres of gravity of imbalance weight and the pertinent bearing axes is required Weights G and G1, amplitude of linear vibration r and distance R have the following relationship: The spherical roller bearing FAG 22320E.T41A with a dynamic load rating of 655 kN is chosen Machining tolerances The locating bearings of. .. lubrication For lubricating the spherical roller bearings at the locating end, the oil thrown off by the gear suffices A flinger ring is provided for this purpose at the opposite end Baffle plates (A) at the housing faces maintain an oil level reaching about the centre point of the lowest rollers The oil level is such that the lower gear and the flinger ring are partly submerged The oil level can be checked... flinger ring and a V-ring in the labyrinth provide sealing at the drive shaft passage 2 1 A A B 1 2 A B Locating bearing Floating bearing Baffle plates Sight glass 98: Bearing mounting of a two -bearing screen with straight-line motion 99 Four -bearing screen The vibration radius of a four -bearing screen is a function of the shaft eccentricity It is not variable; therefore these screens are also called... Further radial clearance reduction results from the different thermal expansion of inner and outer rings in operation Therefore, bearings of radial clearance group C4 (i e radial clearance larger than C3) are mounted To prevent detrimental axial preloading, the inner rings are assembled so that an axial clearance of 0.2 0.3 mm exists between the roller sets of the two bearings and the lips (floating bearing. .. roller bearings mounted in the housings as locating bearings Axial displacement is permitted by two collaterally arranged linear bearings (rollers) which provide support for one of the two housings With this design the amount of friction to be overcome during axial displacement is limited to the rolling contact friction occurring in the linear bearings (coefficient of friction µ ≈ 0.05) Locating bearing. .. N6 The bearing outer rings carry circumferential load and are, therefore, tight fits Since the inner rings are subjected to oscillating loads, it is advisable to fit them tightly onto the shaft as well With non-separable bearings this requirement would make bearing mounting and dismounting extremely complicated Therefore, separable cylindrical roller bearings of design NJ are used Bearing clearance Bearing. .. Due to the high centrifugal forces, the load carrying capacity of the deep groove ball bearings usually used for medium-sized electric motors is not sufficient for this application Vibrator motors are, therefore, supported on cylindrical roller bearings The arrangement shown incorporates two cylindrical roller bearings FAG NJ2306E.TVP2.C4; the dynamic load rating of the bearings is 73.5 kN The adverse... number of inner bearings z = 2; acceleration due to gravity g = 9.81 m/s2 bearings of series 223 are also used The bearing size is dictated by the shaft diameter so that the load carrying capacity is high and fatigue life calculation unnecessary Since these bearings are not subjected to vibration, the standard design with normal clearance is satisfactory In the example shown spherical roller bearings... displacement of the spherical roller bearing To minimize the frictional resistance, the bore of the sleeve is ground and coated with dry lubricant (molybdenum disulphide) For thrust load calculation a coefficient of friction of µ = 0.1 0.15 is used Both bearings are thus safely dimensioned Five cylindrical rollers (80 x 120 mm) each are required for the two linear bearings The hardness of the guide rails... roller bearings FAG 22328E.T41A (dynamic load rating C = 1,220 kN) are chosen Outer bearings The stationary outer bearings are only lightly loaded since the centrifugal forces of the screen box are balanced by counterweights Generally spherical roller Locating bearing Counterweight 99: Four -bearing screen Inner bearings The inner bearings (a locating-floating bearing arrangement ) feature point load on the . BNM3234KR.132887. One of the plummer blocks is designed as the floating bearing (closed on one side, design AL), the other one as the locating bearing (continuous shaft, design BF). The unsplit housings of series. acting as the locating bearing, the other one as floating bearing. The increased radial clearance C3 was selected because of the high speed. The bearing inner rings heat up more than the outer. as outer bearings and FAG 23176K.MB as inner bearings. The pitman bearing arrangement is of the floating bearing type. The outer bearing arrange- ment features a locating bearing at the drive